Multiple characterizations of Listeria monocytogenes sensitive and insensitive variants to divergicin M35, a new pediocin-like bacteriocin

Abstract

Aims: Divergicin M35 is a new class IIa bacteriocin produced by Carnobacterium divergicin M35. The bactericidal activity of this antimicrobial peptide was tested against a set of 11 strains of Listeria monocytogenes isolated from food.

Methods and results: The minimal inhibitory concentration (MIC) was determined by the microdilution method. The strains tested displayed a different level of sensitivity to divergicin M35. L. monocytogenes LSD530, referred to as DivS strain, was the most sensitive and appeared to be inhibited by concentration of divergicin M35 below 0.13 microg ml(-1). The mutant resistant to divergicin M35, called DivM, was obtained from L. monocytogenes LSD530 (DivS) by gradually increasing the amounts of divergicin M35 until 1.3 microg ml(-1). Notably, DivM was stable after 50 generations. DivS parental strain was inhibited by a concentration of 4 microg ml(-1). L. monocytogenes LSD530 was shown to be resistant to divergicin M35 at 1.3 microg ml(-1). Remarkably, in the presence of divalent cations such as Ca(2+), Mg(2+) and Mn(2+), the lethality caused by divergicin M35 was reduced by 0.48, 0.54 and 0.63 log CFU per ml (after 18 h at 30 degrees C), respectively. The total DNA profiles of DivS and DivM were similar. DivS and DivM showed variable sensitivity to antibiotics. The two-dimensional (2-D) electrophoresis of cell wall proteins did not show any significant difference between DivS and DivM strains but their fatty acid composition showed a significant difference in C(16:0) content.

Conclusions: Resistance to divergicin M35 is likely ascribed to modification in cell wall fatty acid composition rather than protein modification.

Significance and impact of the study: This study provides original results contributing to understanding of the resistance of L. monocytogenes to divergicin M35, a new class IIa bacteriocin.